| Abstract: | Free volumes in thermotropic side-chain liquid-crystalline polymers were probed by positron annihilation technique. Lifetime spectra of positrons were measured in the temperature range between 130 and −60°C in cooling. For a nematic liquid-crystalline polymer (polyacrylate), the lifetime of ortho-positronium (τ3) was decreased with decreasing temperature above the glass transition temperature (Tg, 21°C) with larger temperature coefficient than that below Tg. The intensity of ortho-positronium (I3) was constant above Tg. These facts mean that the size of the free-volume holes decreased with the decreasing the temperature but the concentration was almost constant in nematic phase. For a smectic liquid-crystalline polymer (poly(p-methylstyrene) derivative), a discontinuous decrease in the value of τ3 and that of I3 were observed at 107°C, which was the transition temperature from smectic to crystalline phase. Such discontinuous changes were not observed for the polyacrylate specimen. This difference was considered to be attributed to the higher-ordered structure of the smectic phase. © 1996 John Wiley & Sons, Inc. |
